Method for forming nylon strip stock



F b- 12, 1 E. E. MONTROSS METHOD FOR FORMING NYLON STRIP STOCK Filed Aug. 7, 1947 INVENTOR ATTORNEYS Patented Feb. 12, 1952 UNITED STATES PATENT OFFICE METHOD FQRFORMING NYLON STRIP STOCK Eugene E. Montross, Reading, Pa., assignorto The. Rolymerflorporatiem Reading, 2a., a cor- Imitation ofilfennsylvania Application Augusti, 1947, Serial No. 767,282-

of a variety of sections, and isespecially'suited to the production of flat strip stock, either the thickness or-width of which may be varied overa fairly broad range. As a typical example,- thestripstock maybe-.020 in thickness and 1%" inwidth.

Continuous formation of strip stock from nyion has presented certain problems anddifiiculties, especially because of certain of the characteristics of nylon, particularly the fact that this: material has: a sharp melting point and has relatively low viscosity inthe moltencondition.

According to theinv-ention, a method is provided which effectively meets the-special prob lems encountered and which is exceptionally simple, notwithstanding its capability of con-- tinuous production-of strip stock.

The invention further provides for adjustment of' the operating conditions whereby to enable the production of strip: stock of variousdifferent:

sections; for instance various: different widths and thicknesses.

In accordance with the invention, the nylon material, for instance polyhexamethylene adipamide, is heatedabove its 1 melting point r andis:

continuously fed; in molten condition, to the entrance nip of a. pair of rolls maintained at; a

temperature appreciably below the solidification point, whereby to substantially concurrently solidify and roll the molten material;

Howa'the invention isncarried into practice and how the foregoing objects and advantages. are obtained will appear more clearly from: the following descriptionreferring to the accompanying drawing, in which:

Figure 1 is a somewhat diagrammatic, vertical, sectional view through equipment arranged for carrying. out. the present invention;

Figure: 2 is a top plan view of: the equipment,

end of -the .screw shaft. as:- indicatedqat. 62', pro.

iecting'fromtheiendiof: the casingior association with drive: mechanism.. The; ny1on,;,in,- flake, or;

granular form, is introduced into the feeder through the funnel I, and as the material is ad vanced by the screw 5 it is heated to a temperature above its melting point by any appropriate source of heat, such as the inset electrical heating coils 8.

The molten nylon is discharged through a nozzle 9, the discharge end of which is located in close proximity to the entrance nip of a pair of rollslil-I i which are adapted to be mounted by means of supporting shafts l2-I3. Shaft 12'.

is adapted to be driven by a gear I4 associated with any suitable power source, and the two shafts are geared to rotate together by meansof gearing 15. The rolls iii-41 may either becylindrical or grooved or otherwise shaped so as to produce either fiat strip stock or strip stock of shaped section.

Attention is now called to the fact that the rolls iil-i I are mounted within a tank I6, which tank is adapted to contain acooling liquid such as water, for instance up to the level W, as. shown in Figure 1.

The strip of nylon indicated by the letter S, passes downwardly in the tank l6 from the rolls I9-H and under the guide roll l1, and thencein an inclined path to another guide 18, and

' finally out of the tank to a pair of rolls l9-l9,

which latter are preferably driven so as to main-- tain some slight tension on the strip S. The pressure of interengagement and the coefficient: of friction of the rolls i9--l9 are preferablysuch as to provide for slight tensioning of the strip stock, while permitting slippage, due to the coefilcient of friction and pressure ofinterengage. ment.

The guide arrangement I8; may either comprise a non-rotatable guide bar or a rotatable member, as desired. This is also, true of the. guide roll IT.

The tank It is adapted to be supplied; with the water or other cooling liquid through a supply connection 20 and the, tankis provided with an overflow pipe 2!. The overflow or outlet is desirably arranged to provide for regulationof the;

water level maintained in the tank. As an example of one simple expedient for this purpose, the overfiow pipe as shown inthe drawing, comprises an elbow of fairly large diameter, which may be twisted to lower or:raise the discharge end thereof, and thereby establish a lower or higher water level in the tank.

It is, also pointed out that the invention contemplatesadjustment of thewspacegbetween the rolls Ill-l i. This maybe doneby-providing-ar movable support for shaft I3 on which roll H is carried. An appropriate range of adjustment may be secured in this way, notwithstanding the intermeshing gearing [5, since the gear teeth will still function even if the depth of interengagement thereof is varied somewhat.

In operation, the flake or granular nylon is continuously fed into the hopper funnel T and as this material is advanced by the screw 5 it is heated to the molten condition and then is fed through the nozzle 9 for discharge to the rolls Ifll I.

The cross-sectional shape of the discharge orilice of nozzle 9 may be circular, especially in the case of production of strip stock of which the thickness is relatively great as compared with the width. 0n the other hand, in the case of production of strip stock of relatively great width as compared with the thickness thereof, a discharge orifice of somewhat elongated cross-sec- 'tion is preferred, for instance as indicated at 9a in Figure 3, in which case it is positioned with its major axis paralleling the the axes of the rolls.

It is of importance that the discharge orifice of the nozzle 9 be located in close proximity to the rolls Ill-H so that the nylon is delivered to the rolls while still in molten condition. The close proximity of the discharge orifice of the nozzle is also of importance in minimizing exposure of the nylon to the surrounding air while in molten condition. With the rolls at a temperature well below the solidification point of the nylon, the molten material is substantially concurrently solidified and rolled to the desired strip stock section. The temperature of the molten material delivered to the rolls, the temperature at which the rolls are maintained, and. the speed of operation are desirably such that the strip stock is completely solidified as it is delivered from the rolls. In this way the rolls act to perform their rolling function at the time the material is actually changing from the molten to the solid state.

With respect to the manner of cooling the rolls and maintaining the temperature thereof at the desired point, it is mentioned that this may be achieved in a variety of ways, although the employment of a water bath is exceedingly simple and therefore very practical. I have achieved particularly effective results in an arrangement as illustrated, with the water level maintained at or close to the level of the axes of rotation of the rolls l0li. With a water supply of approximately uniform temperature, the temperature of the rolls may be regulated either by regulating the level maintained in the tank or by regulating the speed of circulation. The temperature of the molten nylon and also the speed of operation of the equipment will likewise influence the temperature at which the rolls are maintained, and the several variables above mentioned should all be regulated so that the nylon is completely solidified as it passes through the rolls.

With still further reference to the cooling of the feed rolls Ill-ll, it is mentioned that I have found that under certain conditions of operation, even air cooling will suflice, in which event the water bath It may be completely dispensed with. For most conditions of operation, however, I prefer the employment of a liquid cooling bath for a number of reasons, including the fact that a lower roll temperature is more con veniently provided in this way and the further fact that uniformity of roll temperature may more readily be maintained.

In connection with the matter of temperatures (both of the molten nylon and of the rolls I0--l I) several factors should be kept in mind, as follows:

First note that various of the nylon materials, for example polyhexamethylene adipamide, have solidification or freezing points substantially below the melting points thereof. In the case of polyhexamethylene adipamide, the melting point lies quite sharply at about 508 F., whereas the freezing point lies at about 473 F'. To ensure complete melting of all parts of the material, this particular polyamide should be heated somewhat above 508 F., for instance from about 515 F. to about 550 F. Moreover, with this particular nylon material, the temperature of rolls Ill-ll should be well below 473 F., for instance from about 150 F. to about 350 F. Since the freezing point (473 F.) is well below the melting point, the temperature may be allowed to drop somewhat prior to discharge from the nozzle 9. Indeed I have secured particularly effective results by effecting discharge of the nylon from the nozzle at a temperature below the melting point but above the freezing point.

With any of the high molecular weight synthetic linear polyamides, the temperature of the molten material fed to the rolls is preferably at least 10 F. above the freezing point of the particular polyamide, and the temperature of the rolls l0ll is preferably at least F. below the freezing point of the particular polyamide.

As illustrative of the method, I have produced strip stock (about 1 /2 in width and .020" in thickness) from polyhexamethylene adipamide with rolls of 2.78 diameter water cooled to various temperatures ranging from F. to F. I have made similar strip stock with the rolls merely air cooled and operating at temperatures ranging up to 340 F.

It is of particular advantage that the roll temperature need not be maintained at a critical value, uniform results being obtainable over quite a broad range of roll temperatures. Indeed, I have found that strip stock of highly uniform gauge may readily be made even with substantial variations of roll temperature and even with substantial variations in the temperature of the molten material delivered to the rolls.

The strip stock made according to the invention is characterized by exceptional freedom from porosity, voids or other flaws. In considering one important reason for this, it should be kept in mind that bubbles tend to develop in molten nylon materials, especially at temperatures appreciably above the melting point. The action of the rolls, however, tends to rid the material of bubbles by driving them to the edges of the strip stock being formed. In cases where the margins or edge portions of the strip have excessive porosity, or are otherwise non-uniform, they should be trimmed off.

In addition to polyhexamethylene adipamide, other similar nylon materials may be used in the practice of the invention, for instance polyhexamethylene sebacamide or any other similar high molecular weight synthetic linear polyamide having the characteristics of sharp melting point and relatively low viscosity in the molten condition.

I claim:

1. A method for forming strip stock from synthetic linear polyamides, which method comprises feeding the polyamide in solid particle form into 7 a screw feed device, continuously moving said polyamide through said device, heating said device to melt the polyamide in said device while the polyamide is being advanced therein and thereby provide for delivery of a stream of molten polyamide from the screw feed device, and directing said stream of molten polyamide to the entrance nip of a pair of rotative forming rolls maintained at a temperature below the freezing point of the polyamide to efiect formation and solidification of the strip, the rate of melting of the polyamide in the screw feed device being substantially the same as the rate of feed of the molten polyamide to the entrance nip of the forming rolls.

2. A method according to claim 1 in which the stream of molten polyamide delivered to the forming rolls is of elongated cross section with the long axis thereof paralleling the axes of the rolls.

6 3. A method according to claim 1 and further including the step of slitting a finished strip from the area intermediate the edge portions of the strip delivered from the forming rolls.

EUGENE E. MONTROSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,212,772 Graves Aug. 27, 1940 2,214,397 Austin Sept. 10, 1940 2,244,208 Miles June 3, 1941 2,336,159 Bent Dec. 7, 1943 2,340,834 Hanson Feb. 1, 1944 2,352,861 Pierce July 4, 1944 

